Electromechanical transducer



Sept. 9, 1958 J. F. WOOD ELECTROMECHANICAL TRANSDUCER 2 Shaots-Sheed 1 Filed July 28, 1954 p 1958 J. F. WOOD 2,851,541

ELECTROMECHANICAL TRANSDUCER Filed July 28; 1954 2 Sheets-Sheet 2 ELECTROMECHANICAL TRANSDUCER John F. Wood, Buchanan, Mich., assignor to Electro- Voice, Incorporated, Buchanan, Mich.

Application July 28, 1954, Serial No. 446,255

6 Claims. ,(Cl..1-7,9-10,0.41)

The present invention relates to electromechanical transducing devices, and more specifically to phonograph cartridges.

In order to minimize the cost in producing a phonograph cartridge, it is necessary to reduce the amount of hand-work to a minimum. One of the operations in assembling a phonograph cartridge that requires costly hand manipulations in the presently made devices is the connection of electrical contacts to the signal generating element of the phonograph cartridge. The signal generating element of conventional phonograph cartridges is often a piezoelectric ceramic element, and the leads from the element are often soldered to the conductive surfaces of the element. In another conventional construction, the leads are connected to plates which are maintained in pressure contact with the conductive surfaces of the signal generating element by the force of a compliant rubber mounting pad. The necessary hand work in performing these operations is made more difiicult by the fact that this work must generally be done before the cartridge case is closed.

It is an object of the present invention to provide an electromechanical transducer which may be readily fabricated and which is adaptable to production line techniques.

It is a further object of the present invention to provide a phonograph cartridge in which the electrical contacts to the signal producing element are maintained by a flexible member.

It is also an object of the present invention to provide electrical contact with the signal generating element of an electromechanical transducer by a clip which when inserted in position forms a pressure contact with the signal generating element without having a deleterious effect upon the electrical operation of the signal generating element.

Other and further objects of the present invention will become readily apparent to the man skilled in the art from a further reading of the present disclosure, particularly when viewed in the light of the drawings, in which:

Figure l is an elevational view of an electromechanical transducer in the form of a phonograph cartridge constructed according to the teachings of the present invention;

Figure 2 is a plan View of the phonograph cartridge illustrated in Figure 1;

Figure 3 is a sectional view taken along the line 3-3 of Figure 2.

'-'Figurc 4 is asectional view taken along the line 4-4 of Figure 1;

Figure 5 is an end elevational view of the phonograph cartridge as illustrated in Figure 1;

Figure 6 is a front elevational view of the phonograph cartridge as illustrated in Figure 1;

Figure 7 is a fragmentary sectional view taken normal to the axis of the signal producing element illustrating the position of the contact member; and

atent 2,851,541 Patented Sept. 9, 1958 Figure 8 is an isometric View of one of the spring contact members- The principal elements of the phonograph cartridge, as illustrated in the figures, are a housing 10, a stylus 12 supported within the housing 10 and extending to the exterior thereof, a signal producing element 14, and means to make electrical contact with the surfaces of the signal generating element 14, namely contact members 16. Many types of signal generating elements 14 have been used in phonograph pick ups. The present invention may be utilized with any type of signal generating element which provides electrically conducting surfaces which are suitable for terminals. In the case of quartz crystal elements or piezoelectric ceramic elements, opposite surfaces of the element become charged with the signal voltage, and the present invention is therefore clearly suitable to these types of elements. Also, the figures illustrate a pair of styli 12 attached to the signal generating element 14. It is also clear that the invention maybe practiced with a single stylus, or with more than two styli, as the applications for the phonograph cartridge require.

The body 18 is constructed of an electrically insulating material, such as polyethylene plastic, and may be considered as having two adjacent portions 18 and 20, al-

though it is to be understood that the body is constructed of a single unit. One of the portions may be termed the head 20 and contains the styli 12, and the other portion may be termed the base 18. The base 18 has a gen erally rectangular cross section throughout its length, and the head 20 has a slightly larger rectangular cross section in the region adjacent to the base 18. The head 20 however is generally wedge shaped and tapers to a point 22. A rectangular cavity 24 extends into the body 10 from the point 22 of the head 20. The cavity 24 does not extend through the body 10, but stops adjacent to the end 26 opposite to the head 20. This end 26 of the cavity 24 has a smallercross section than the rest of the cavity 24. The signal generating element 14 is inserted into the body 10 through the mouth of the cavity 24, and it is secured axially therein by a compliant sleeve 28 which is snugly disposed between the base 18 and the signal generating element 14 in the end portion 26 of the cavity 24. In the particular construction of the phonograph cartridge which is to be described in detail throughout this disclosure, the compliant sleeve 28 is constructed of rubber and is cemented to the signal generating element 14 and to the base 18 of the body 10. A styli supporting member 30 is attached to the opposite end of the signal generating element 14 by means of a recess 32 into which the signal producing element 14 is disposed and secured, as by cement. The stylus supporting member 38 is a fiat member provided with a pair of surfaces on opposite sides of the axis of the signal gen erating element 14 tapering toward that axis, these surfaces being designated 34 and 36. The surface of the member 38 adjacent to the point 22 of the head 20 of the body 10 is disposed normal to the axis of the signal generating element 14 and intersects the tapered surfaces 34 and 36 The styli 12 are disposed centrally in the surfaces 34 and 36, and are set in recesses 40 in the member 30. In the particular embodiment of the invention described throughout this specification, the two styli 12 are disposed normally to the tapered surfaces 34 and 36 which are disposed at an angle of 35 degrees relative to the axis of the signal generating element 14.

A damping bar 42 extends from the base 18 of the body 10 to the signal generating element 14 about midway between the styli mounting member 38 and the resilient sleeve 28. The damping bar 42 is also con structed of resilient material, and in the particular con- -a substantially straight portion.

struction it is constructed of rubber. The damping bar 42 is disposed normal to the axis of the signal generating element 14 and roughly parallel to the signal produced displacement of the signal generating element 14.

The base 18 of the body is provided with a pair of apertures 44 and 46 on opposite sides of the signal producing element 14. A pair of spring contact elements 43 traverse the apertures 44 and 46, and contact the surfaces of the signal generating element 14 which become electrically charged responsive to the displacement of the stylus 12. It is to be noted that in the case of piezoelectric crystals, the surfaces which generate the potential responsive to the displacement are normal to the displacement, and hence normal to the styli. Each of the spring contacts 4S is secured in position by means of a pair of hooks 52 and a clip 54 which are disposed at opposite ends of the contacts 48. The hooks 52 extend about the apertures 44 and 46 into the cavity 24, and the clips 54 extend over protruding ribs 56 at the end of the body 10 to secure the contacting elements 48 in position.

As clearly illustrated in Figure 8, each spring contact 48 has a fiat elongated central portion 58 which is longitudinally divided into three strips at one end, the outer two strips being bent into an acute angle relative to the central portion, forming the hooks 52. The central strip, designated 60, extends outwardly from the hooks 52 and is bent to have a curved portion 62, followed by The end 64 of the straight portion has a small curvature. The flat portion adjacent the end 64 is disposed in pressure contact with the plated contact area 16 of signal generating element 14. This occurs near the compliant support 28 where the element 14 hasa minimum of motion. The contacting elements 48 are constructed of resilient electrically conducting material and may be used to make electrical contact from the signal generating element 14 to other portions of the circuit, either by a pressure fit against the spring contacts 48 or by connecting the contacts 48 to terminals of any conventional type. It is to be noted that the spring contacts 48 contact the signal generating element 14 in its region of smallest excursion, that is in the region of the signal producing element 14 which produces the least excursion for a given displacement of the stylus 12. In this manner, the spring contacts do not appreciably affect the characteristic electrical operation of the signal generating element 14 when the signal generating element 14 is constructed of piezoelectric materials.

A phonograph cartridge constructed in the manner described above may be assembled as follows. The styli 12 are first inserted into the recesses 40 in the styli holding member 30 and secured therein. The styli holding member 30 is thereupon attached to the end of the signal generating element 14 by cementing the element 14 into the recess 32 in the member 30. Next, the resilient sleeve 28 and the snubbing bars 42 are attached to the signal generating element 14 in the proper places, as by cement, and the entire assembly is then inserted into the cavity 24 of the body 10. Before inserting this assembly into the cavity, the restricted portion 26 of the cavity is coated with cement so that the resilient sleeve 28 will be secured within the body 10. In like manner, the two resilient bars 42 are attached to the body 10. At this point, all that remains to be done is to snap the spring contacts 48 into the apertures 44 and 46 and about the protruding ribs 56.

From the foregoing disclosure, the man skilled in the art will readily perceive the ease with which the electromechanical transducer constructed according to the teachings of this invention may be assembled. He will also devise other methods and devices for making contact with the signal producing element of an electromechanical transducer within the spirit and scope of the present invention. It is therefore intended that the scope of the present invention be not limited by the foregoing disclosure, but rather only by the appended claims.

What' is claimed is:

1. An electromechanical transducer comprising a body having a cavity therein, said body also being provided on each of two parallel surfaces with an aperture extending transversely into the cavity, an element disposed within the cavity adapted to generate an electrical potential between a pair of surfaces thereof in response to a mechanical displacement thereof, and means to make electrical contact with opposite surfaces of the signal generating element comprising a pair of members constructed of resilient sheet material clipped to the exterior of the body, said members including integral spring contact elements extending through the apertures and making pressure contact directly With the signal generating element.

2. An electromechanical transducer comprising a body having a cavity extending therein from one end, said body having a pair of apertures on opposite sides thereof extending into the cavity, a piezoelectric element disposed within the cavity adapted to produce an electrical signal on opposite surfaces thereof in response to a mechanical displacement thereof, said piezoelectric element carrying at one end a phonograph stylus, and means on the exterior of said body to make direct electrical contact with the piezoelectric element comprising a pair of members constructed of resilient sheet material clipped to the body, each of said members including a spring contact extending through one of the apertures in the body into the cavity and making pressure contact with one of the surfaces of the piezoelectric element.

3. An electromechanical phonograph transducer comprising a body having a cavity extending therein from one end, said body having an aperture on each of two opposite sides extending into the cavity, a piezoelectric element disposed within the cavity adapted to generate an electrical signal in response to a mechanical displacement thereof, said piezoelectric element carrying at one end a phonograph stylus, and means on the exterior of said body to make electrical contact with the signal generating element comprising a pair of members each constructed of resilient sheet material having a hook extending within the aperture at one end and a clip extending over the end of the body at the other end, said member also having an integral spring contact extending through the aperture and making pressure contact directly with the signal generating element.

4. An electromechanical transducer comprising a body having a cavity therein, said body having a pair of apertures on opposite sides thereof extending into the cavity and a pair of outwardly extending ribs adjacent one end of the body, a piezoelectric element disposed within the cavity and attached at one end to the body, said element being adapted to produce an electrical potential on opposite surfaces thereof in response to a displacement thereof, the voltage producing surfaces of the piezoelectric element confronting the apertures in the body, and means to make electrical contact with the voltage producing surfaces of the piezoelectric element comprising a pair of members constructed of resilient sheet material, each member having a hook at one end extending within one of the apertures and a fiat portion disposed adjacent to the exterior of the body, the other end of each member having a resilient bend toward the hook disposed over the ribs at the end of the body, each member including a spring contact extending beyond the hook in the member, through the adjacent aperture, and generally parallel to the adjacent surface of the piezoelectric element, the portion of each of said members generally parallel to the piezoelectric element being in pressure contact with the piezoelectric element.

a pair of apertures on opposite sides thereof and a pair of outwardly extending ribs adjacent to the peripheries of one end of the body, said ribs being adjacent to the sides of the cavity having the apertures therein, a piezoelectric element disposed within the cavity adapted to produce an electrical signal on opposite surfaces thereof, the voltage producing surfaces of the piezoelectric element confronting the apertures in the body, a sleeve constructed of resilient material disposed between one end of the piezoelectric element and the body, said sleeve being attached to both the body and the piezoelectric element, and means to provide electrical contact with the piezo electric element comprising a pair of members constructed of resilient material, each member having a pair of spaced hooks at one end extending within the aperture and clips at the other end extending over the end of the body, said members being provided With spring contacts extending from between the hooks, through the adjacent aperture and forming pressure contact with the confronting surfaces of the piezoelectric element.

6. A phonograph cartridge comprising a body having a cavity extending therein from one end, said body having a pair of apertures on opposite sides thereof extending into the cavity and a pair of ribs :at the end thereof opposite to the mouth of the cavity adjacent to the apertured Walls of the body, a piezoelectric element disposed Within the cavity adapted to produce an electrical potential across opposite surfaces thereof in response to a mechanical displacement thereof, a sleeve constructed of resilient material disposed about one end of the piezoelectric element and attached thereto, said sleeve also being in contact with the walls of the cavity and attached thereto thereby mounting the piezoelectric element along the axes of elongation of the cavity, a pair of snubbing bars constructed of resilient material disposed between the potential producing surfaces of the piezoelectric element and the body, and means to make electrical contact with each of the potential producing surfaces of the piezoelectric element comprising a member constructed of resilient material having a hook at one end extending into the aperture in contact with the body, a central portion adjacent to the hook conforming to the outer surface of the body between the aperture and the end of the body, a bent portion extending toward the hook disposed over one of the ribs at the end of the body, and a spring contact extending from the hook portion through the aperture, into the cavity and terminating in a portion generally parallel to the potential producing surfaces of the piezoelectric element, said portion being in contact with said surfaces at a point adjacent the resilient sleeve supporting one end of said element.

References Cited in the file of this patent UNITED STATES PATENTS 2,138,036 Kunze Nov. 29, 1938 2,416,876 Kuenstler Mar. 4, 1947 2,429,414 Kuenstler Oct. 21, 1947 2,471,625 Johnstone May 31, 1949 2,549,757 Corbett Apr. 24, 1951 2,565,586 Bauer Aug. 28, 1951 2,639,393 Birt May 19, 1953 2,650,991 Ketchledge Sept. 1, 1953 2,703,343 Sneprangers Mar. 1, 1955 FOREIGN PATENTS 180,787 Great Britain June 8, 1922 

